Superhydrophobic Research Articles

Hybrid superhydrophobic/hydrophilic patterns deposited on glass by laser-induced forward transfer method for efficient water harvesting

In recent years, the combination of factors such as growing population and global climate change has resulted in freshwater shortages. Therefore, water harvesting from the atmospheric fog in order to produce freshwater supply inspired by nature has received much attention. The water harvesting capability of the creatures is significantly based on the combination of both wettability states on their surfaces. In this study, a facile physicochemical hybrid method was used for the fabrication of glass surfaces with contrast wettability. First, fractal and regular repeated geometric patterns were deposited on a glass substrate using brass sheet as donor material by laser induced forward transfer (LIFT) method. Subsequently, stearic acid (SA) treatment was used to convert the wettability of the superhydrophilic (SHL) deposited patterns on glass to superhydrophobic. In order to investigate the effect of the shape of designed patterns on glass surfaces in the water harvesting efficiency, the amount of collected water for a period of time from untreated hydrophilic (HL) glass, superhydrophobic (SHB) glass and hybrid superhydrophobic/hydrophilic (SHB-HL) surfaces were measured. The obtained results indicate that the hybrid of superhydrophobic and hydrophilic regions and selecting the optimal pattern can improve the water harvesting performance by up to 300%.

Surface effects on Sub-cooled pool boiling for smooth and laser-ablated silicon surfaces

Smooth and laser-ablated silicon surfaces with wettability ranging from SHI (super-hydrophilic) to SHO (super-hydrophobic) are tested in subcooled pool boiling of water. The experiment focuses on the observation of bubble phenomena using a high-speed camera and the measurement of surface temperature using an infrared camera. The formation and departure of vapor bubbles from the surfaces are found to vary significantly with the surface wettability. Nucleate boiling curves show that both the heat transfer coefficient and the critical heat flux increase with the surface wettability changing from SHO to SHI. For the hydrophilic surfaces (smooth and textured), the heat transfer coefficient increases with the heat flux. For the hydrophobic surfaces (smooth and textured), the heat transfer coefficient decreases with the increasing heat flux. The effect of the surface wettability is quantitatively assessed using the surface-fluid factor. It is found that the factor's value increases with the surface wettability changing from SHI to SHO. The surface effect for the hydrophilic surfaces remains relatively constant over the nucleate boiling range, whereas for the hydrophobic surfaces the effect shows significant dependency on the heat flux. These findings are also revealed from the boiling tests on a biphilic surface consisting of a SHO region and a SHI region.

Triboelectric nanogenerators for marine energy harvesting and sensing applications

Triboelectric nanogenerators (TENG) are emerging as a potential technology in the wave energy harvesting domains due to their attractive characteristics like robust structure, ease of material selection, facile fabrication, high sensitivity, and high output. Since TENG enables the harvesting of random, multidirectional, low-frequency mechanical motions, its applicability can be easily extended to harvest the most underutilized renewable energy source - wave energy. This review article discusses the latest developments in marine energy harvesting and self-powered sensors using TENG. The study covers the basic understanding of TENG, its development pathways, working principle, and standard operational modes and focuses on the reported works on wave energy harvesting and self-powered sensing applications. Though various studies have been reported in lieu of wave energy harvesting, the immense possibilities of improvement of structure and materials do exist. More exploration of bionic structures and superhydrophobic materials for liquid-solid interface TENG will be a breakthrough in renewable energy harvesting.

A Review on Nanocellulose and Superhydrophobic Features for Advanced Water Treatment.

Globally, developing countries require access to safe drinking water to support human health and facilitate long-term sustainable development, in which waste management and control are critical tasks. As the most plentiful, renewable biopolymer on earth, cellulose has significant utility in the delivery of potable water for human consumption. Herein, recent developments in the application of nanoscale cellulose and cellulose derivatives for water treatment are reviewed, with reference to the properties and structure of the material. The potential application of nanocellulose as a primary component for water treatment is linked to its high aspect ratio, high surface area, and the high number of hydroxyl groups available for molecular interaction with heavy metals, dyes, oil-water separation, and other chemical impurities. The ability of superhydrophobic nanocellulose-based textiles as functional fabrics is particularly acknowledged as designed structures for advanced water treatment systems. This review covers the adsorption of heavy metals and chemical impurities like dyes, oil-water separation, as well as nanocellulose and nanostructured derivative membranes, and superhydrophobic coatings, suitable for adsorbing chemical and biological pollutants, including microorganisms.

Preparation of durable multi-functional coating silk fabrics with persistent fragrance release, antibacterial, fluoride-free superhydrophobic and self-cleaning properties

Multi-functional coating textiles with high value-added can be applied widely in daily life. However, the durability of multi-functional textiles is of particular interest both in academia and industrial field for years. In this work, the durable multi-functional silk fabric with persistent fragrance release, antibacterial, fluoride-free superhydrophobic and self-cleaning properties was successfully fabricated via a rapid polymerization of dopamine, in-situ growth of silver nanoparticles (Ag NPs) and coated of the barrier layer of polydimethylsiloxane (PDMS). The composite coating was composed of polydopamine (PDA), essential oil microcapsules (EOM), PDMS and Ag NPs. The prepared fabric displayed persistent fragrance release properties, with the fragrance storage rate achieved 55.56 % at 50 °C for 30 d. In addition, the multi-functional silk fabric had good antibacterial activity against E. coli and S. aureus with antibacterial rates of 97.33 % and 96.95 %, respectively, but also showed fluoride-free super hydrophobic and self-cleaning properties. The corresponding static contact and roll-off angles were 151° and 9°, respectively. More importantly, the produced coating exhibited robustly mechanical durability super hydrophobicity properties against 100 cycles of sandpaper rubs or 10 h of simulated water washing and washing durability antibacterial against 50 cycles of water washing. This study provides a simple and effective method for the durable multi-functional coating silk fabric, making it highly promising for high-end product.

Synthesis of Superhydrophobic Cellulose Stearoyl Ester for Oil/Water Separation.

Developing fluorine-free superhydrophobic and biodegradable materials for oil/water separation has already become an irresistible trend. In this paper, we designed two biopolymer oil/water separation routes based on cellulose stearoyl ester (CSE), which was obtained via the acylation reaction between dissolving pulp and stearoyl chloride homogeneously. The CSE showed a superhydrophobic property, which could selectively adsorb oil from the oil/water mixture. Additionally, the CSE was emulsified with an oxidized starch (OS) solution, and the resulting latex was used to impregnate commercial, filter base paper, finally obtaining a hydrophobic and oleophilic membrane. The SEM revealed the membrane had hierarchical micro/nanostructures, while the water contact angle indicated the low surface energy of the membrane, all of which were attributed to the CSE. The membrane had high strength and long durability due to the addition of OS/CSE, and the separation efficiency was more than 99% even after ten repeated uses.

In situ formation of polymethylsiloxane nanofilaments on pristine cotton stalk with natural interconnected pores for rapid and recyclable organic solvents absorption

The creation of a superhydrophobic surface with simplified hydrophobic steps still faces great challenges. Herein, an in situ one-step hydrophobic strategy of growing polysiloxane nanofilaments onto pristine rod-shaped cotton stalk (CS) surface is used to prepare a new bulk superhydrophobic CS absorbent. The rich hydroxyl groups contained in CS directly polymerize with the silanols generated by the hydrolysis of methyltrichlorosilane on CS surface to form polysiloxane nanofilaments, leading to a change in the wettability of the CS surface. This strategy makes the water contact angle of the prepared absorbent as high as 161°, representing exceptional water repellency. Benefiting from the unique natural interconnected pore structures, the absorbent takes only 20 s to reach absorption equilibrium, showing rapid absorption performance toward organic solvents. The absorbent still maintains good absorption capacity even after 20 absorption-desorption cycles, holding excellent recyclability. The proposed hydrophobic modification approach simplifies the steps to the surface hydrophobization of CS, which provides a new strategy for the preparation of biomass-based superhydrophobic materials.

Facile Fabrication of Superhydrophobic Graphene/Polystyrene Foams for Efficient and Continuous Separation of Immiscible and Emulsified Oil/Water Mixtures.

Three-dimensional superhydrophobic/superlipophilic porous materials have attracted widespread attention for use in the separation of oil/water mixtures. However, a simple strategy to prepare superhydrophobic porous materials capable of efficient and continuous separation of immiscible and emulsified oil/water mixtures has not yet been realized. Herein, a superhydrophobic graphene/polystyrene composite material with a micro-nanopore structure was prepared by a single-step reaction through high internal phase emulsion polymerization. Graphene was introduced into the polystyrene-based porous materials to not only enhance the flexibility of the matrix, but also increase the overall hydrophobicity of the composite materials. The resulting as-prepared monoliths had excellent mechanical properties, were superhydrophobic/superoleophilic (water/oil contact angles were 151° and 0°, respectively), and could be used to continuously separate immiscible oil/water mixtures with a separation efficiency that exceeded 99.6%. Due to the size-dependent filtration and the tortuous and lengthy micro-nano permeation paths, our foams were also able to separate surfactant-stabilized water-in-oil microemulsions. This work demonstrates a facile strategy for preparing superhydrophobic foams for the efficient and continuous separation of immiscible and emulsified oil/water mixtures, and the resulting materials have highly promising application potentials in large-scale oily wastewater treatment.

Adhesion behavior of different droplet on superhydrophobic surface of cotton fabric based on oxygen plasma etching

Oxygen plasma etching followed with spraying of hydrophobic suspension containing SiO2 nanoparticles were used to construct superhydrophobic cotton fabric, and the adhesion behavior of the superhydrophobic surface to deionized water, dye liquor, sterile defibrinated sheep blood, and simulated blood solutions was studied and evaluated in focus. Results of the present study showed the water contact and water slip angles of the superhydrophobic cotton fabric were 158.6° and 7.3° with 5 wt% of hexadecyltrimethoxysilane (HDTMS). The plasma etching imparted uniform strip grooves on the fiber, which together with the deposition of SiO2 nanoparticles constituted a dual-scale rough structure on the fabric surface. FTIR analysis showed the successful combination of HDTMS and SiO2 nanoparticles and covering on the cotton surface. This superhydrophobic surface possessed hydrophobic effect even after 35 times of abrasion and immersion in strong acid or alkali solutions for 8 h. The surface tension and viscosity of simulated blood and sterile defibrinated sheep blood (SDSB) were similar, with a contact angle of only 139.7° and a slip angle above 20°. And their adhesion forces were calculated by the Cassie-Baxter equation to be 30.93 and 37.88 μN. Moreover, the droplets placement of simulated blood and SDSB on the superhydrophobic surface for 2 h caused trace adhesion but no penetration. This indicated that the superhydrophobic surface had anti-adhesion performance to the liquids. In conclusion, it was evident that the superhydrophobic fabric has good application prospects in the field of textiles for daily life and medical protection.

3D printed superhydrophobic structures for sustainable manufacturing benefits: An overview

Superhydrophobic properties have been present in nature for many millennia before human beings discovered their true capabilities and utilized them to revolutionize modern societies. The most familiar form of hydrophobicity found in nature is that of the lotus leaf, where its ultra-low water adhesion and self-cleaning properties make it one of the best hydrophobic elements formed naturally. Since its discovery, artificially created superhydrophobic elements have been used in many industries --maritime, automobile, and medical -- due to their self-cleaning, antibacterial, and corrosion-prevention properties. However, for a surface to become superhydrophobic, it must possess a greater roughness. To achieve this, microscopic- or nanoscopic-level modifications must be made to the surface through various experimentations. For a surface to be considered superhydrophobic, it must have a water contact angle greater than 150°. One cost-effective method of manufacturing superhydrophobic materials is three-dimensional (3D) printing (additive manufacturing), which has been gaining popularity in the recent past. A 3D printing design is initially created using computer-aided design (CAD) software. Then, the design information is transferred to a 3D printer through digital slicing of the CAD design. 3D printing allows the printing of objects with various functionalities at pre-designed locations in the object, so it is important to investigate these phenomena. This paper provides an overview of several studies that were conducted to achieve superhydrophobicity through the 3D printing process. The following section of the manuscript includes an introduction, literature review, methods of increasing surface roughness for superhydrophobicity, market-available 3D printing materials, and their applications, discussion on 3D printing technologies and concluding remarks.

Super pressure-resistant superhydrophobic fabrics with real self-cleaning performance

SummaryDetergents are extensively used for laundry, causing significant negative impacts on water bodies, plants and animals. Superhydrophobic fabrics are promising to reduce detergent consumption but suffer from low pressure resistance. Here, we report super pressure-resistant superhydrophobic fabrics prepared using polysiloxane modified SiO2 nanoparticles with epoxy groups. The fabrics show real self-cleaning performance, essentially different from the conventional self-cleaning property of solid particles loosely placed on superhydrophobic surfaces. The contaminated fabrics by various stains can be completely cleaned by home machine laundering without using any detergent whereas the traditional superhydrophobic fabrics cannot. This is owing to excellent abrasion and washing durability, low liquid adhesion force, superior pressure-resistance and vapor-resistance of the fabrics, originating from the low surface energy and dense micro-/nanostructure. Moreover, the superhydrophobic fabrics can be scaled up using the conventional fabric finishing line with low cost. The superhydrophobic fabrics will help significantly reduce the global detergent consumption.

Preparation of superhydrophobic conductive CNT/PDMS film on paper by foam spraying method

Paper-based materials are widely used in agriculture, industry and daily life because of their biodegradability, sustainability, biocompatibility and low cost. However, due to the hydrophilic nature of plant fibers in paper-based materials, the mechanical properties of paper will be reduced after absorbing water, thus limiting its application field. In this paper, carbon nanotubes/polydimethylsiloxane (CNT/PDMS) films with hydrophobicity and conductivity were prepared on filter paper by foam spraying method. Firstly, CNT and PDMS were added into water and stirred vigorously, and CNT/PDMS foam homogenate was prepared by foaming agent and stabilizer. Then, the homogenate was sprayed on the filter paper with a spray gun, and the multilevel rough structure was prepared on the paper. The results showed that the contact angle of the sample surface is greater than 150° when the spraying amount is 0.4-CNT, 0.6-CNT and 0.8-CNT, and the contact angle of 0.6-CNT is 156.33°, which is the largest. The drops on the surface of the sprayed sample have good bounce and self-cleaning performances. In addition, benefiting from the excellent conductivity of CNT, the particles composed of CNT and PDMS contact each other on the surface of the sample, forming a conductive network. The aforementioned properties will broaden the application scenarios of paper-based superhydrophobic materials.

A facile strategy to prepare robust self-healable superhydrophobic fabrics with self-cleaning, anti-icing, UV resistance, and antibacterial properties

A robust self-healable superhydrophobic fabric is fabricated via in situ diazonium radical polymerization. By employing diazonium salts, Cu powder, and ascorbic acid, the hierarchical NO2phene-Cu2O/Cu7Cl4(OH)10H2O, CF3phene-Cu2O/Cu7Cl4(OH)10H2O, and DCF3phene-Cu2O/Cu7Cl4(OH)10H2O micro/nanostructures with different morphologies—nano spindles, nano rods, and nano particles—are constructed on the surface of cotton fabric with the driving force of π-π stacking and hydrophilic/hydrophobic interactions under ambient conditions. Owing to the strong covalent bond, π-π stacking, and hydrophobic interaction, the CF3phene-Cu2O/Cu7Cl4(OH)10H2O@cotton fabric (CF3Ph-CuxO@CF) surface could maintain the superhydrophobicity even after 20 cycles of laundering and 1500 cycles of abrasion, showing excellent mechanical durability. The developed CF3Ph-CuxO@CF exhibits outstanding oil/water separation ability with reliable recyclability and stability, allowing it for effective separation of clean water from either heavy or light oil contaminants. In addition, it is further shown that the superhydrophobic fabric also demonstrated excellent self-cleaning, self-healing, ultraviolet (UV) protection, anti-icing, and antibacterial capabilities. It is hence believed these valuable functions could significantly enhance the practical feasibility of the superhydrophobic fabric in various application scenarios.

Bioinspired Robust Water Repellency in High Humidity by Micro-meter-Scaled Conical Fibers: Toward a Long-Time Underwater Aerobic Reaction.

Superhydrophobic surfaces have suffered from being frequently penetrated by micro-/nano-droplets in high humidity, which severely deteriorates their water repellency. So far, various biological models for the high water repellency have been reported, which, however, focused mostly on the structural topology with less attention on the dimension character. Here, we revealed a common dimension character of the superhydrophobic fibrous structures of both Gerris legs and Argyroneta abdomens, featured as the conical topology and the micro-meter-scaled cylindrical diameter. In particular, it can be expressed by using a parameter of rp/l > 0.75 μm (r, l, and p are the radius, length, and apex spacing between fibers, respectively). Drawing inspiration, we developed a superhydrophobic micro-meter-scaled conical fiber array with a rather high rp/l value of 0.85 μm, which endows ultra-high water repellency even in high humidity. The micro-meter-scale asymmetric confined space between fibers enables generating a big difference in the Laplace pressure enough to propel the condensed dews away, while the tips help pin the air pocket underwater with a rather long life over 41 days. Taking advantage, we demonstrated a sustainable underwater aerobic reaction where oxygen was continuously supplied from the trapped air pocket by a gradually diffusing process. As a parameter describing both the dimension character and structural topology, the rp/l offers a new perspective for fabricating superhydrophobic fibrous materials with robust water repellency in high humidity, which inspires the innovative underwater devices with a robust anti-wetting performance.

Fabrication of adsorbents with enhanced CuI stability: Creating a superhydrophobic microenvironment through grafting octadecylamine

In atmospheric conditions, CuI is easily oxidized to CuII due to the coexistence of moisture and oxygen. The poor oxidation inhibition of CuI restricts the practical application of CuI-containing materials. Herein we introduce an approach to construct a superhydrophobic microenvironment in CuI-functionalized metal–organic frameworks by coordinatedly grafting organic amine compounds onto open metal sites (OMSs), which can hinder the accessibility of moisture to pores thereby enhancing the stability of CuI. As a proof of concept, MIL-101(Cr) with abundant OMSs and octadecylamine (OA) with long hydrophobic alkyl groups are used as carrier and surface coating. As superhydrophobic porous materials, the resultant CuIM-OA exhibits improved CuI stability in addition to retaining high crystallinity and intact porosity while almost all CuI is oxidized in hydrophilic CuIM upon exposure in a humid atmosphere for 30 h. CuIM-OA owns excellent adsorption desulfurization performance (ADS) with regard to thiophene, benzothiophene, and 4,6-dimethyl dibenzothiophene. Even from hydrated fuel, the adsorption performance of CuIM-OA maintains well while the adsorption capacity of CuIM decreases to 7% after 4 cycles. The remarkable moisture resistance, CuI stability, and high porosity make the current adsorbent CuIM-OA highly promising for the practical ADS process.

Facile fabrication of durable superhydrophobic fabrics by silicon polyurethane membrane for oil/water separation

Nowadays, oil contamination has become a major reason for water pollution, and presents a global environmental challenge. Although many efforts have been devoted to the fabrication of oil/water separation materials, their practical applications are still hindered by their weak durability, poor chemical tolerance, environmental resistance, and potential negative impact on health and the environment. To overcome these drawbacks, this work offers a facile method to fabricate the eco-friendly and durable oil/water separation membrane fabrics by alkaline hydrolysis and silicon polyurethane coating. The X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy results demonstrate that silicon polyurethane membrane could be coated onto the surface of hydrolyzed polyester fabric and form a micro-/nano-scaled hierarchical structure. Based on this, the modified fabric could have a stable superhydrophobic property with a water contact angle higher than 150°, even after repeated washing and mechanical abrasion 800 times, as well as chemical corrosion. Moreover, the modified fabrics show excellent oil/water separation efficiency of up to 99% for various types of oil–water mixture. Therefore, this durable, eco-friendly and cost-efficient superhydrophobic fabric has great potential in large-scale oil/water separation.

Preparation and surface modification of magnesium-based sound absorbing materials via a low-temperature vapor deposition

The poor durability of lightweight cement due to hydrophilic property and porous microstructure limits its extensive application. In this study, a superhydrophobic magnesium-based sound absorbing materials (Mg-SAM) have been prepared using basic magnesium sulfate cement as the matrix material and then modified by a low-temperature vapor deposition (LTVD). The results reveal that an ultrathin film of perfluorodecyltriethoxysilane (PFDTS) can be gently deposited on the surface of Mg-SAM with a water contact angle higher than 150° via a low temperature (65 °C) heating process. The modification mechanism of LTVD can be described as the formation of a self-assembled fluorine-containing film through the condensation reaction between silanols and the hydroxyl groups on the surface of Mg-SAM. The noise reduction coefficient and mechanical strength of Mg-SAM with a density of 280 kg·m−3 reach 0.7 and 1.8 MPa respectively without any change after LTVD treatment. This facile, low-cost LTVD technique is a promising approach for large-scale modification of porous materials.

Preparation and particle size effects study of sustainable self-cleaning and durable silicon materials with superhydrophobic surface performance

Superhydrophobic materials with surface drying, self-cleaning, and antibiological pollution characters are broadly used in biotechnology, medicine, and shipbuilding sectors. In this paper, micro-nano silica is modified using a silane-based coupling agent. An organosilicon compound is grafted to the silica surface to obtain a superhydrophobic material with low surface energy. The results show that the superhydrophobic material with a 20 nm particle size silica modified with vinyltriethoxysilane (VTES-SiO2) offers the best properties with a contact angle of 163.32° and a rolling angle of smaller than 3°. Compared with the raw material, the treated silica reveals superhydrophobicity under nano conditions with a rolling angle smaller than 3°. The wettability of the prepared material does not decrease after being placed in the air for 3 months. Moreover, it still maintains self-cleaning performance after being placed in water for one month, showing the potential of long-term use of the material. The prepared materials provide excellent superhydrophobic properties while is environmentally friendly. Thus, this study delivers potential value for the preparation of environmentally friendly superhydrophobic materials with broad application prospects of superhydrophobicity and self-cleaning characters.

Fabrication of superhydrophobic and flame-retardant polyethylene terephthalate fabric through a fluorine-free layer-by-layer technique

Abstract Polyethylene terephthalate (PET) fabric materials are broadly applied in daily life. However, on one hand, they suffer problem of easy contamination by dust owing to their hydrophilicity, which largely reduce their lifetime. On the other hand, their inflammability will bring many potential safety hazards. Therefore, in this paper, PET fabric material with superior superhydrophobicity and flame retardance through a fluorine-free layer-by-layer (LBL) method was developed, which effectively extended its lifetime and range of applications. The LBL technique was realized through assembly of the mixed polyelectrolytes include chitosan (CS), phytic acid (PA), and ammonium polyphosphate (APP) for only two bilayers (BL), which endowed the fabric superior fire retardance. A final layer consisted of steel slag (SS) particles and octadecylamine (ODA) were further assembled onto the flame-retardant fabric, which successfully gave rise to superior superhydrophobicity with water contact angle (WCA) of 155° and water sliding angle (WSA) of 2°. Compared with the pure fabric, the limited oxygen index (LOI) values of the coated fabric were enhanced from 19.8% to 29.2%. The finally obtained fabric also showed excellent self-cleaning and anti-fouling capabilities. It could be used to highly efficiently separate various oil–water mixtures. It also could endure long-time heating treatment at high temperature of 180 °C without affecting the superhydrophobicity and flame retardance. This method was fluorine-free and made good use of waste SS particles. Such fabric was believed to find vary promising applications in water repellence, self-cleaning, flame retardance, anti-fouling, and liquid separation fields.

Study on the Influence of Polymer/Particle Properties on the Resilience of Superhydrophobic Coatings.

Enhancement in the resilience of superhydrophobic coatings is crucial for their future applicability. However, the progress in this aspect is currently limited due to the lack of a consistent resilience analysis methodology/protocol as well as the limited understanding of the influence of the materials components on the resultant coating performance. This study applies a quantitative analysis methodology involving image analysis and mass tracking and utilizes it to investigate how the properties of coating components can influence coating resilience. The factors examined were changing the molecular weight/tensile strength of poly(vinylchloride)/poly(dimethylsiloxane) (PVC/PDMS) polymers and changing the size of the roughening particles. In addition to the examination of resilience data to evaluate degradation patterns, three-dimensional (3D) mapping of the scratches was performed to obtain an insight into how material removal occurs during abrasion. The results can indicate preferential polymer selection (using higher-molecular-weight polymers for PVC) and optimal particle sizes (smaller particles) for maximizing coating resilience. The study, although focused on superhydrophobic materials, demonstrates wide applicability to a range of areas, particularly those focused on the development of high-strength coatings.